Your problem is most likely something stuck on the scanner glass that is blocking that part of the scanner glass, causing the black line down the sheet. Open up the machine and remove the roller to get to the scanner glass. Look very closely at the glass and see if anything is stuck to it; even a small speck might cause this problem. The black line on the page will be the same place to look on the glass for any . If alcohol on a cotton swab doesn't help, try using a small piece of paper and wipe off the glass with it. You can also use a fingernail to scrape off that part of the glass. Don't worry, a fingernail won't harm the glass.

Hope that helps!